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Abstract:

A signal transceiver includes a connector for receiving a signal, a
band-pass filter coupled to the connector for filtering the signal, a
front-end module for demodulating the signal and an adaptive impedance
switch circuit coupled between the band-pass filter and the front-end
module for switching an impedance value between the band-pass filter and
the front-end module.

Claims:

1. A signal transceiver, comprising: a connector, for receiving a signal;
a band-pass filter, coupled to the connector, for filtering the signal; a
front-end module, for demodulating the signal; and an adaptive impedance
switch circuit, coupled between the band-pass filter and the front-end
module, for switching an impedance value between the band-pass filter and
the front-end module.

2. The signal transceiver of claim 1, wherein the adaptive impedance
switch circuit comprises: an input terminal, coupled to the band-pass
filter, for receiving the signal; an output terminal, coupled to the
front-end module, for outputting the signal to the front-end module; a
voltage input circuit, for providing an input voltage; a frequency
resonant circuit, coupled to the input terminal and the voltage input
circuit, for adjusting the impedance value; and a bias circuit, coupled
between the front-end module and a node connected by the input terminal,
the voltage input circuit and the frequency resonant circuit, for
converting a voltage value of the signal.

3. The signal transceiver of claim 2, wherein the voltage input circuit
comprises: a voltage input terminal, for receiving the input voltage; a
switcher, coupled to the voltage input terminal, for switching a state of
the voltage input circuit; and a first resistor, coupled to the switcher.

4. The signal transceiver of claim 2, wherein the frequency resonant
circuit comprises: a second resistor, having one terminal coupled to the
voltage input circuit and the input terminal; an inductor, having one
terminal coupled to the second resistor; a first capacitor, having one
terminal coupled to the inductor; a first switch, having one terminal
coupled between the second resistor and the inductor; a second capacitor,
having one terminal coupled to the first switch; a second switch, having
one terminal coupled to the second capacitor; and a third capacitor,
having one terminal coupled between the inductor and the first capacitor,
and another terminal coupled between the second capacitor and the second
switch.

5. The signal transceiver of claim 4, further comprising: a third
resistor in parallel with the second capacitor.

6. The signal transceiver of claim 4, wherein a resistance value of the
second resistor is determined according to an element connected to the
connector.

7. The signal transceiver of claim 2, wherein the bias circuit comprises:
a third switch; and a fourth resistor, coupled between the third switch
and the output terminal.

8. An adaptive impedance switch circuit for switching an impedance value
in a signal transceiver, the adaptive impedance switch circuit
comprising: an input terminal, for receiving a signal; an output
terminal, for outputting the signal; a voltage input circuit, for
providing an input voltage; a frequency resonant circuit, coupled to the
input terminal and the voltage input circuit, for adjusting the impedance
value; and a bias circuit, coupled between the output terminal and a node
connected by the input terminal, the voltage input circuit and the
frequency resonant circuit, for converting a voltage value of the signal.

9. The adaptive impedance switch circuit of claim 8, wherein the voltage
input circuit comprises: a voltage input terminal, for receiving the
input voltage; a switcher, coupled to the voltage input terminal, for
switching a state of the voltage input circuit; and a first resistor,
coupled to the switcher.

10. The adaptive impedance switch circuit of claim 8, wherein the
frequency resonant circuit comprises: a second resistor, having one
terminal coupled to the voltage input circuit and the input terminal; an
inductor, having one terminal coupled to the second resistor; a first
capacitor, having one terminal coupled to the inductor; a first switch,
having one terminal coupled between the second resistor and the inductor;
a second capacitor, having one terminal coupled to the first switch; a
second switch, having one terminal coupled to the second capacitor; and a
third capacitor, having one terminal coupled between the inductor and the
first capacitor, and another terminal coupled between the second
capacitor and the second switch.

11. The adaptive impedance switch circuit of claim 10, further
comprising: a third resistor in parallel with the second capacitor.

12. The adaptive impedance switch circuit of claim 10, wherein a
resistance value of the second resistor is determined according to an
element connected to the signal transceiver.

13. The adaptive impedance switch circuit of claim 8, wherein the bias
circuit comprises: a third switch; and a fourth resistor, coupled between
the third switch and the output terminal.

Description:

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a signal transceiver and adaptive
impedance switch circuit, and more particularly, to a signal transceiver
and adaptive impedance switch circuit capable of effectively improving
return loss when the signal transceiver operates in a power-off state.

[0003] 2. Description of the Prior Art

[0004] Ethernet over Coax (EoC) is a transmission technology in which the
Ethernet signals are transmitted over a coaxial cable. The objective of
EoC is to connect to the Internet or wideband data transmission utilizing
existing cable television infrastructures, which is compatible with
existing cable (or satellite TV) broadcast signals, to reach the goal of
simultaneously transmission of data signals over the same coaxial cable.
Among the EoC methods, the multimedia network standard developed by the
multimedia over coax alliance (MoCA) has functionalities of high speed
and high quality of service (QoS) which are required for the glitch-free
streaming media. According to the multimedia network standard, signals
can be sent to each client through the existing coaxial cable, such that
the client only needs a signal transceiver to demodulate the signals to
obtain services.

[0005] Please refer to FIG. 1, which is a schematic diagram of a
conventional signal transceiver 10. The signal transceiver 10 includes a
connector 100, a band-pass filter (BPF) 102 and a front-end module 104.
Usually, the signal transceiver 10 is implemented with a set-top box
(STB). The connector 100 connects one coaxial cable, for receiving
signals including a MoCA signal, which is transmitted via the coaxial
cable. The BPF 102 is utilized for filtering the signal, so as to pass
the signal within a frequency band. For example, the range of the
frequency band of the MoCA signal provided by the U.S. satellite TV
service provider DIRECTV® is from 475 MHz to 625 MHz. If only the MoCA
signal needs to be passed, the frequency range of the BPF 102 should be
set from 475 MHz to 625 MHz. The front-end module 104 is utilized for
demodulating the signal through the BPF 102. In general, the front-end
module 104, which is usually integrated into an integrated circuit (IC),
includes circuits such as a transmitter-receiver, a power amplifier and
an attenuator, etc.

[0006] Please refer to FIG. 2A and FIG. 2B, which are schematic diagrams
of the return loss between the connector 100 and one coaxial cable (not
shown) connected to the connector 100 within a frequency band of 475-625
MHz when the signal transceiver 10 operates in a power-on and power-off
state, respectively. By comparing FIG. 2A and FIG. 2B, it can be seen
that within the frequency band of 475-625 MHz, the minimum return loss of
the signal transceiver 10 in the power-off state is nearly 7.6 dB, which
is 3.4 dB lower than in the power-on state (nearly 11 dB). As can be seen
from the above, if the signal transceiver 10 operates in the power-off
state, the system may encounter performance degradation due to over-low
return loss.

SUMMARY OF THE INVENTION

[0007] It is therefore a primary objective of the present invention to
provide a signal transceiver and adaptive impedance switch circuit
capable of effectively improving return loss when the signal transceiver
operates in a power-off state.

[0008] An embodiment of the present invention discloses a signal
transceiver, which includes a connector for receiving a signal, a
band-pass filter coupled to the connector for filtering the signal, a
front-end module for demodulating the signal and an adaptive impedance
switch circuit coupled between the band-pass filter and the front-end
module for switching an impedance value between the band-pass filter and
the front-end module.

[0009] The embodiment of the present invention further discloses an
adaptive impedance switch circuit for switching an impedance value in a
signal transceiver. The adaptive impedance switch circuit includes an
input terminal for receiving a signal; an output terminal for outputting
the signal; a voltage input circuit for providing an input voltage; a
frequency resonant circuit coupled to the input terminal and the voltage
input circuit for adjusting the impedance value; and a bias circuit
coupled between the output terminal and a node connected by the input
terminal, the voltage input circuit and the frequency resonant circuit
for converting a voltage value of the signal.

[0010] These and other objectives of the present invention will no doubt
become obvious to those of ordinary skill in the art after reading the
following detailed description of the preferred embodiment that is
illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 is a schematic diagram of a conventional signal transceiver.

[0012] FIG. 2A is a schematic diagram of the return loss between the
connector shown in FIG. 1 and a coaxial cable connected to the connector
within a specific frequency band when the signal transceiver shown in
FIG. 1 operates in a power-on state.

[0013] FIG. 2B is a schematic diagram of the return loss between the
connector shown in FIG. 1 and a coaxial cable connected to the connector
within a specific frequency band when the signal transceiver shown in
FIG. 1 operates in a power-off state.

[0014] FIG. 3 is a schematic diagram of a signal transceiver according to
an embodiment of the present invention.

[0016] FIG. 4B is a schematic diagram of the current direction when the
switcher of the adaptive impedance switch circuit shown in FIG. 3
switches to a conducted state.

[0017] FIG. 4C is a schematic diagram of the current direction when the
switcher of the adaptive impedance switch circuit shown in FIG. 3
switches to a non-conducted state.

[0018] FIG. 5A is a schematic diagram of the return loss between the
band-pass filter and the front-end module shown in FIG. 3 within a
specific frequency band when the signal transceiver shown in FIG. 3
operates in the power-on state.

[0019] FIG. 5B is a schematic diagram of the return loss between the
band-pass filter and the front-end module shown in FIG. 3 within a
specific frequency band when the signal transceiver shown in FIG. 3
operates in the power-off state.

[0020] FIG. 6A is a schematic diagram of the return loss between the
connector shown in FIG. 3 and a coaxial cable connected to the connector
within a specific frequency band when the signal transceiver shown in
FIG. 3 operates in the power-on state.

[0021] FIG. 6B is a schematic diagram of the return loss between the
connector shown in FIG. 3 and a coaxial cable connected to the connector
within a specific frequency band when the signal transceiver shown in
FIG. 3 operates in the power-off state.

DETAILED DESCRIPTION

[0022] Please refer to FIG. 3, which is a schematic diagram of a signal
transceiver 30 according to an embodiment of the present invention. The
signal transceiver 30 includes a connector 300, a band-pass filter (BPF)
302, an adaptive impedance switch circuit 304 and a front-end module 306.
The connector 300, the BPF 302 and the front-end module 306 are
respectively similar to the connector 100, the BPF 102 and the front-end
module 104 of the conventional signal transceiver 10, and thus the same
components are not narrated hereinafter for simplicity. The adaptive
impedance switch circuit 304, which is coupled to the BPF 302 and the
front-end module 306, is utilized for switching an impedance value
between the BPF 302 and the front-end module 306.

[0023] Please refer to FIG. 4A, which is one implementation of the
adaptive impedance switch circuit 304 shown in FIG. 3. In FIG. 4A, the
adaptive impedance switch circuit 304 includes an input terminal 400, an
output terminal 402, a voltage input circuit 404, a frequency resonant
circuit 406 and a bias circuit 408. The input terminal 400, which is
coupled to the BPF 302, is used for receiving the signal passed through
the BPF 302. The output terminal 402, which is coupled to the front-end
module 306, is used for outputting the filtered signal to the front-end
module 306. The voltage input circuit 404, which is used for providing
the input voltage Vcc, includes a voltage input terminal 410, a switcher
SW and a resistor R1. Thereamong, the voltage input terminal 410 is used
for receiving the input voltage Vcc, the switcher SW is used for
switching the status of the voltage input circuit 404, and the resistor
R1 is coupled to the switcher SW. The frequency resonant circuit 406,
which is coupled to the input terminal 400 and the voltage input circuit
404, is used for adjusting the impedance value between the BPF 302 and
the front-end module 306. The frequency resonant circuit 406 includes the
resistors R2 and R3, the capacitors C1, C2 and C3, the inductor L1 and
the switches D2 and D3. The bias circuit 408 is coupled between the
output terminal and a node connected by the input terminal 400, the
voltage input circuit 404 and the frequency resonant circuit 406. The
bias circuit 408 includes the resistor R4 and the switch Dl. The
aforementioned switches D1, D2 and D3 are preferably implemented using
diodes, and the resistance of the resistor R2 may be determined according
to an element (e.g. coaxial cable) connected to the connector.

[0024] FIG. 4B and FIG. 4C illustrate the current flow directions in the
adaptive impedance switch circuit 304 when the switcher SW switched to
the conducted and non-conducted states, respectively. As shown in FIG.
4B, when the switcher SW switches to a conducted state (i.e. power-on
state), the switches D1, D2 and D3 are conducted, and thus there are two
current flows with different directions (illustrated as arrows in FIG.
4B): one passes through the switch D1, and the other passes through the
resistor R2, the switch D2, the capacitor C2 and the switch D3 to a
ground terminal. The capacitor C3 with higher capacitance and the
resistor R3 with higher resistance may be designed to avoid reverse
current flow. As shown in FIG. 4C, when the switcher SW switches to a
non-conducted state (i.e. power-off state), the switches D1, D2 and D3
are all non-conducted, such that the current flow passes through the
resistor R2, the inductor L1 and the capacitor C1 to the ground terminal
(illustrated as arrow in FIG. 4C). That is, the path combined with the
resistor R2, the inductor L1 and the capacitor C1 is short-circuited.

[0025] The adaptive impedance switch circuit 304 according to the
embodiment of the present invention is an independent circuit, which is
coupled between the BPF 302 and the front-end module 306. Alternatively,
the adaptive impedance switch circuit 304 and the front-end module 306
may be integrated into an integrated circuit.

[0026] Please refer to FIG. 5A and FIG. 5B, which are schematic diagrams
of the return losses between the BPF 302 and the front-end module 306
within the frequency band 475-625 MHz when the signal transceiver 30
operates in the power-on state and power-off state, respectively. By
comparing FIG. 5A and FIG. 5B, it can be seen that when the signal
transceiver 30 operates in the power-off state, the minimum return loss
between the BPF 302 and the front-end module 306 within the frequency
band 475-625 MHz is nearly 20 dB, which is 9 dB higher than that in the
power-on state (nearly 11 dB). As mentioned above, when the signal
transceiver 30 operates in the power-off state, the return loss between
the BPF 302 and the front-end module 306 will increase.

[0027] Please refer to FIG. 6A and FIG. 6B, which are schematic diagrams
of the return losses between the connector 300 and a coaxial cable (not
shown) connected to the connector 300 within the frequency band 475-625
MHz when the signal transceiver 30 operates in the power-on state and
power-off state, respectively. By comparing FIG. 6A and FIG. 6B, it can
be seen that when the signal transceiver 30 operates in the power-off
state, the minimum return loss between the connector 300 and the coaxial
cable (not shown) within the frequency band 475-625 MHz is nearly 11.5
dB, which is 0.5 dB higher than that in the power-on state (nearly 11
dB). As mentioned above, when the signal transceiver 30 operates in the
power-off state, the return loss between the connector 300 and the
coaxial cable (not shown) may be kept higher than that in the power-on
state.

[0028] Note that, the aforementioned FIG. 5B and FIG. 6B only illustrate
that within the frequency band 475-625 MHz, the minimum return loss of
the signal transceiver 30 can effectively increase when the signal
transceiver 30 operates in the power-off state. Those skilled in the art
may adjust the characteristics of the elements in the adaptive impedance
switch circuit 304 according to various frequency bands, such that the
minimum return losses in various frequency bands can effectively
increase.

[0029] The return loss of the prior art signal transceiver may decrease
when the signal transceiver operates in the power-off state, causing the
system performance to degrade. In comparison, the signal transceiver of
the present invention can switch the impedance value between the
band-pass filter and the front-end module by utilizing the adaptive
impedance switch circuit when the signal transceiver operates in the
power-off state, so as to improve the return loss effectively.

[0030] To sum up, the signal transceiver of the present invention can
improve the return loss effectively when the signal transceiver operates
in a power-off state, and therefore the system performance is improved.

[0031] Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made while
retaining the teachings of the invention. Accordingly, the above
disclosure should be construed as limited only by the metes and bounds of
the appended claims.